X-ray generator and exposure apparatus

ABSTRACT

An X-ray generator for generating plasma and X-ray emitted from the plasma includes a unit for generating the plasma, and plural reflection optical systems for introducing the X-ray through different optical paths.

“This application is a continuation of co-pending U.S. application Ser.No. 11/246,485, filed on Oct. 7, 2005.”

BACKGROUND OF THE INVENTION

The present invention relates to an X-ray generator that generates theX-ray and extreme ultraviolet (“EUV”) light, and an exposure apparatushaving the same.

In manufacturing such a fine semiconductor device as a semiconductormemory and a logic circuit in photolithography technology, a reductionprojection exposure apparatus has been conventionally employed whichuses a projection optical system to project a circuit pattern formed ona mask (reticle) onto a wafer, etc. to transfer the circuit pattern. Itis also important for the fine processing to use the exposure lighthaving a shorter wavelength, to make uniform the light intensity thatKoehler-illuminates the reticle, and to make uniform the effective lightsource distribution as an angular distribution of the exposure lightthat illuminates the reticle and the wafer.

The minimum critical dimension to be transferred by the projectionexposure apparatus or resolution is proportionate to a wavelength oflight used for exposure. Thus, a projection optical apparatus using theEUV light with a wavelength of about 10 nm to about 15 nm much shorterthan that of the UV light (referred to as “EUV exposure apparatus”hereinafter) has been developed. The EUV exposure apparatus typicallyuses a laser plasma light source. It irradiates a laser beam to a targetmaterial to generate plasma for use as the EUV light. The EUV exposureapparatus also typically uses a discharge plasma light source thatgenerates the plasma and generates the EUV light by introducing gas tothe electrode for discharging. For example, prior art include JapanesePatent Publications, Application Nos. 2002-174700 and 2004-226244.

However, the laser plasma light source generates not only the EUV lightbut also flying particles called debris from the target material. Inaddition, the debris is emitted from the supply mechanism that suppliesthe target material. The debris also spreads from the electrode materialin the discharge plasma light source. The debris causes contaminations,damages, and lowered reflectivity of optical elements, making uneven thelight intensity and deteriorating the throughput. Accordingly, U.S. Pat.No. 6,359,969 arranges a debris mitigation system between a lightemitting point and a mirror so as to remove the debris.

The debris mitigation system is designed to remove the debris andtransmit the EUV light, but actually it shields part of the EUV lightand lowers the light intensity and throughput. In addition, the debrismitigation system shields the EUV light of a certain angle range, makesuneven the angular distribution and lowers the imaging performance. Forexample, FIG. 3 schematically shows a relationship between the lightintensity per unit solid angle and the angle from the optical axis nearthe light source outlet. E1 is energy taken in by the optical system.The minimum angle θ₁ is determined, as shown in FIG. 4, by an areashielded by the debris mitigation system, and the maximum angle θ₂ isdetermined by the downstream optical system. Without the debrismitigation system, the minimum angle θ₁ is smaller, and the angularuniformity and the light intensity that depends upon a product betweenthe angle and the light intensity improves, but the mirror would getdamaged by the debris.

BRIEF SUMMARY OF THE INVENTION

Accordingly, it is an exemplary object of the present invention toprovide an X-ray generator and an exposure apparatus, which improve theuniformity of each of the light intensity and the angular distributionof the exposure light.

An X-ray generator according to one aspect of the present invention forgenerating plasma and X-ray emitted from the plasma includes a unit forgenerating the plasma, and plural reflection optical systems forintroducing the X-ray through different optical paths.

An exposure apparatus according to another aspect of the presentinvention includes the above X-ray generator, an illumination opticalsystem for illuminating a reticle having a pattern with X-ray generatedby said X-ray generator, and a projection optical system for projectingthe pattern of the reticle illuminated by said illumination opticalsystem, onto an object to be exposed.

A device manufacturing method according to still another aspect of thepresent invention includes the steps of exposing an object using theabove exposure apparatus, and developing the object exposed.

Other objects and further features of the present invention will becomereadily apparent from the following description of the preferredembodiments with reference to accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view of an X-ray generator (EUV lightsource) according to one aspect of the present invention.

FIG. 2 is a schematic sectional view for explaining a problem when theEUV light source shown in FIG. 1 uses only a first optical system.

FIG. 3 is a view of a light intensity distribution near the light sourceoutlet in the structure shown in FIG. 2.

FIG. 4 is a view of a light intensity distribution near the light sourceoutlet in the structure shown in FIG. 1.

FIG. 5 is a schematic sectional view of one embodiment of the structureshown in FIG. 2.

FIG. 6 is a view of a light intensity distribution at the light sourceoutlet in the structure shown in FIG. 5.

FIG. 7 is a view of a light intensity distribution near the light sourceoutlet in one embodiment of the structure shown in FIG. 1.

FIG. 8 is a schematic sectional view of an EUV light source as avariation according to the first embodiment of the present invention.

FIG. 9 is a schematic sectional view of an EUV light source according toa second embodiment of the present invention.

FIG. 10 is a schematic block diagram of an exposure apparatus accordingto one aspect of the present invention.

FIG. 11 is a flowchart for explaining manufacture of devices (such assemiconductor chips such as ICs and LCDs, CCDs, and the like).

FIG. 12 is a detail flowchart of a wafer process as Step 4 shown in FIG.11.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the accompanying drawings, a description will be givenof an X-ray generator (EUV light source) 10 according to thisembodiment. Here, FIG. 1 is a partial section of the EUV light source10. The EUV light source 10 includes, in a vacuum chamber 12, a plasmagenerating means that is not shown in FIG. 1 and will be describedlater, a debris mitigation system 14, and first and second opticalsystems 20 and 30 that introduce the EUV light through different opticalpaths. Thus, the EUV light source 10 has plural optical systems, makesuniform the angular distribution, and increases the light intensity ofthe light source.

The first optical system 20 is a condenser optical system that includesa spheroid mirror and condenses the X-ray (or EUV light) generated fromthe plasma generating point PL. One of the focal points of the firstoptical system 20 is the plasma generating point PL, and the other isthe light source outlet O. A light that connects a center of the plasmagenerating point PL to a center of the light source outlet O correspondsto the optical axis OA. The acceptable solid angle is determined by thedebris mitigation system 14 and the downstream optical system.

The second optical system 30 is an optical system that enhances thelight intensity of the light source outlet O and the angulardistribution uniformity. More specifically, the second optical system 30supplements the light intensity and the angular distribution of the EUVlight at the light source outlet O corresponding to the angular rangeshielded by the debris mitigation system 14. The second optical system30 includes a spheroid mirror 32 and a hyperboloid mirror 34. The numberof reflections is once in the first optical system 20, whereas thenumber of reflections is twice in the second optical system 30.Therefore, the number of reflections is different between these opticalsystems. One of the focal points of the second optical system 30 is alsothe plasma generating point PL, and the other is also the light sourceoutlet O. More specifically, the spheroid mirror 32 has one focal pointat the plasma emitting point PL, and the other focal point F on theoptical axis. The hyperboloid mirror 34 has the focus points at both theplasma emitting point PL and the light source outlet O. Thus, the firstand second optical systems 20 and 30 have approximately the samecondensing point, where a phrase “approximately the same” intends tocover tolerance. The second optical system 30 is arranged at a positionthat does not shield the first optical system 20.

This embodiment assumes that the plasma emitting point PL uniformlydistributes on the focal plane, and the EUV light emits isotropicallyfrom each location. It also assumes that the first optical system 20ideally images, at an image point or the light source outlet O, theplasma emitting point PL of the object point. Therefore, the imageuniformly circularly distributes at the image position, and the angulardistribution of the EUV light does not depend upon the location. Thereflectance of the first optical system 20 is set to R.

From the above assumptions, the brightness at the light source outlet Ois expressed by IR [W/mm²/sr/nm] irrespective of the capturing opticalsystem, where I [W/mm²/sr/nm] is the brightness of the emission at theplasma emitting point PL. Since an image has a fixed size S at the lightsource outlet O captured by the optical system downstream from the lightsource, the light intensity per solid angle at the light source outlet Ois IRS [W/sr/nm]. Therefore, a difference of the light intensity persolid angle at the light source outlet O is only the reflectance.

If there is only the first optical system 20, the debris mitigationsystem 14 shields the light and forms an area A that does not includethe reflected light, for example, as shown in FIG. 2. FIG. 3 is anangular distribution of the EUV light emitted from the light source. E1is the energy captured by the first optical system 20. However, when thesecond optical system 30 is properly designed and its reflectance is setto R′, the angular distribution can be corrected as shown in FIG. 4. InFIG. 4, E1 is the energy captured by the first optical system 20, and E2is the energy captured by the second optical system 30. In FIG. 4, E1denotes the light intensity distribution similar to that in FIG. 3, andthe light intensity distribution E2 is extended by an angular zone fromθ₀ to θ₁. Thereby, the light intensity increases, the throughputincreases, and the more uniform angular distribution in the range fromθ₀ to θ₂ improves the imaging characteristic.

The capturing amount of the EUV light is expressed by a product (oretendue) between the solid angle and the size. The etendue [mm²·sr] isdefined as (solid angle captured by the optical system)×size. Theetendue of 1 or smaller is preferable for exposure of a size of 100 nmor smaller.

First Embodiment

A description will now be given of the concrete structure of FIG. 1.First, as shown in FIG. 5, in the state where only the first opticalsystem 20 exists, the plasma emitting point PL uniformly distributes ina circle with Φ0.5 mm on the focal plane, and the plasma brightness of50 [W/mm²/sr/nm]. For example, it is assumed by taking the debrisremoving capability into account the debris mitigation system 14disclosed in U.S. Pat. No. 6,359,969 has a size of Φ100 mm. The imagehas a size of 10 mm² and a solid angle of 0.1 sr (etendue=1 [mm²·sr]) asa result of capture by the optical system downstream from the lightsource. Table 1 shows parameters of the first optical system 20determined in terms of the size of the plasma emitting point, the sizeof the debris mitigation system 14, and the etendue: TABLE 1 FIRSTOPTICAL SYSTEM (SPHEROID MIRROR) 20 DISTANCE BETWEEN FOCAL POINTS 1000mm LENGTH OF MAJOR AXIS 1200 mm LENGTH OF MINOR AXIS 660 mm ANGLEBETWEEN OPTICAL 90°-144° AXIS AND LIGHT INCIDENT UPON MIRROR 5 sr SOLIDANGLE ANGLE BETWEEN OPTICAL 3.4°-10° AXIS AND REFLECTED LIGHT SOLIDANGLE 0.1 sr

As shown in FIG. 6, the angular distribution at the light source outlethas IRS=300 [W/sr/nm], θ₁=3.4° and θ₂=10° in FIG. 3. Therefore, no lightexists due to shielding by the debris mitigation system 14 from 0° to3.4° from the optical axis OA, and the light exists from 3.4° to 10°.The image at the light source outlet O has a size of about 10 mm², and asolid angle of 0.1 sr, and thus the etendue of about 1 [mm² ·sr]. Theenergy per unit solid angle of the EUV light emitted from the lightsource becomes 300 [W/sr/nm], where the reflectance of the mirror is0.6. The total energy captured by the first optical system 20 andemitted from the light source is 300 [W/sr/nm]×0.1 [sr]=30 [W/nm].

Accordingly, the second optical system 30 is configured as shown in FIG.1 by combining the spheroid mirror 32 and the hyperboloid mirror 34 soas to supplement the angular range between 0°. and 3.4°. The EUV lightemitted from the plasma emitting point PL is captured by the secondoptical system 30, and forms a light source image at the light sourceoutlet. Table 2 shows one example of parameters of the second opticalsystem 30. TABLE 2 SECOND OPTICAL SYSTEM 30 SPHEROID HYPERBOLOID MIRROR32 MIRROR 34 DISTANCE BETWEEN FOCAL 370 mm 630 mm POINTS LENGTH OF MAJORAXIS 700 mm LENGTH OF MINOR AXIS 660 mm DISTANCE BETWEEN APEXES 440 mmANGLE BETWEEN OPTICAL AXIS 7°-21° AND LIGHT INCIDENT UPON MIRROR ANGLEBETWEEN OPTICAL AXIS 0.75°-3.4° AND REFLECTED LIGHT SOLID ANGLE 0.6 sr0.01 sr

Due to the second optical system 30, the light exists in the rangebetween 0.75°-and 3.4°, as shown in FIG. 7. The image at the lightsource outlet O by the second optical system 30 has a size of about 10mm² and a solid angle of 0.01 sr. Thus, the energy per unit solid angleof the EUV light emitted from the light source becomes 180 [W/sr/nm],where the reflectance of each of the spheroid and hyperboloid mirrors 32and 34 is 0.6. The total energy captured by the second optical systemand emitted from the light source is 180 [W/sr/nm]×0.01 [sr]=1.8 [W/nm].This corresponds to θ₀=0.75 and IR′S=180 in FIG. 4.

As a result of that the first and second optical systems 20 and 30 aresimultaneously used, the angular distribution of the energy per unitsolid angle is as shown in FIG. 7, and the uneven angular distributionis corrected. The increasing rate of the total energy is 1.8 [W/nm]/30[W/nm]=0.06, and the light intensity increases by about 6%.

While the illustrative parameters of the second optical system 30 areshown in the table, the number of configurations of the second opticalsystem 30 is not one even if it combines the spheroid mirror 32 and thehyperboloid 34. The image to be captured by the downstream illuminationoptical system has a size of 10 mm² and a solid angle of 0.01 sr from 0°to 3.4°. Therefore, the maximum etendue that can be captured by thesecond optical system 30 and fed to the following optical system is 100[mm²]×0.01 sr=0.1 [mm² sr]. The second optical system may have anarbitrary configuration as long as it captures the etendue of 0.1 [mm²sr] or greater from the plasma, and supplements the angular distributionbetween 0° and 3.4°.

For example, the EUV light source 10A having a second optical system 30Ahaving a configuration shown in FIG. 8 has the same effect. Table 3shows parameters of the second optical system 30A. TABLE 3 SECONDOPTICAL SYSTEM 30A SPHEROID HYPERBOLOID MIRROR 32A MIRROR 34A DISTANCEBETWEEN FOCAL 100 mm 630 mm POINTS LENGTH OF MAJOR AXIS 700 mm LENGTH OFMINOR AXIS 690 mm DISTANCE BETWEEN APEXES 440 mm ANGLE BETWEEN 24°-24°OPTICAL AXIS AND LIGHT INCIDENT UPON MIRROR ANGLE BETWEEN OPTICAL0.75°-3.4° AXIS AND REFLECTED LIGHT SOLID ANGLE 3 sr 0.01 sr

Second Embodiment

Alternatively, an EUV light source 10B having a second optical system30B that includes a plane mirror 32B and a mirror 34B having a curvaturemay be used. The focal point of the second optical system 30B accordswith two focal points of the first optical system 20, i.e., the plasmaemitting point PL and the light source outlet O. The mirrors 32B and 34Bin the second optical system 30 do not have a revolving body, butpreferably have a rotational symmetry with respect to the optical axis.The number of reflections of the second optical system 30B is notlimited to twice, but the smaller number of reflections is preferablewhen the energy attenuation due to the reflection is considered. Thisembodiment is similar to the first embodiment in that the second opticalsystem 30B does not shield the optical path of the first optical system20.

Third Embodiment

The second optical system 30 may include plural mirrors each having acurvature. The focal points of the second optical system 30 accord withthe two focal points of the first optical system 20, i.e., the plasmaemitting point PL and the light source outlet O. The number ofreflections of the second optical system is not limited to twice, butthe smaller number of reflections is preferable when the energyattenuation due to the reflection is considered. This embodiment issimilar to the first embodiment in that the second optical system 30does not shield the optical path of the first optical system 20.

Fourth Embodiment

Referring now to FIG. 10, a description will be given of the X-raygenerator that has a debris mitigation system of this embodiment and theexposure apparatus 100 having the same. Here, FIG. 10 is a schematicblock diagram of a structure of the exposure apparatus 100.

The inventive exposure apparatus 100 is a projection exposure apparatusthat exposes a circuit pattern of a reticle 120 onto an object 140 usingthe EUV light with a wavelength of 13.4 nm as exposure light in astep-and-scan or step-and-repeat manner. This exposure apparatus issuitable for a lithography process less than submicron or quartermicron, and the present embodiment uses the step-and-scan exposureapparatus (also referred to as a “scanner”) as an example. The“step-and-scan”, as used herein, is an exposure method that exposes areticle pattern onto a wafer by continuously scanning the wafer relativeto the reticle, and by moving, after a shot of exposure, the waferstepwise to the next exposure area to be shot. The “step-and-repeat” isanother mode of exposure method that moves a wafer stepwise to anexposure area for the next shot every shot of cell projection onto thewafer.

The exposure apparatus 100 includes an illumination apparatus 110, areticle stage 125 that supports and mounts the reticle 120, a projectionoptical system 130, a wafer stage 145 that supports and mounts theobject 140 to be exposed, an alignment detecting mechanism 150, and afocus position detecting mechanism 160.

The illumination apparatus 110 uses arc-shaped EUV light, for example,with a wavelength of 13.4 nm corresponding to an arc-shaped field of theprojection optical system 130 to illuminate the reticle 120, andincludes an EUV light source 112 and illumination optical system 114.

The EUV light source 112 according to this embodiment is a laser plasmalight source that irradiates a laser beam LL to a target T, andgenerates plasma and the EUV light EL radiated from the plasma. The EUVlight source 112 may apply any one of the above EUV light sources 10 to10B. The EUV light source 112 includes a laser light source part 40 thatirradiates the laser beam LL, an optical system 50 that introduces thelaser beam LL to the target T, and a target supply unit 60, in additionto the above structure of the EUV light source 10. FIG. 10 omits adetailed configuration of the EUV light source 10 for illustrationpurposes.

The laser beam LL emitted from the laser light source part is condensedby the optical system 50, and irradiated onto the target T. The target Tmay include copper, tin, aluminum and other metal materials, or Xe gas,droplets and cluster. For example, the target T is intermittentlysupplied as Xe droplets from the target supply unit 60 insynchronization with the emissions of the laser beam LL of the laserlight source part 40. The energy from the laser beam LL generates thehigh-temperature and high-density plasma from the target T, and emitsthe EUV light from the plasma 1. The EUV light is collected by the firstoptical system 10, and supplied to the following illumination opticalsystem 114.

The optical system 50 includes a lens, a mirror, a plane-parallel plateglass, etc., and serves as part of the vacuum diaphragm of the vacuumchamber 12. A laser introduction window 54 that transmits the laser beamLL to the vacuum chamber 12 is part of the optical system 50. Theoptical system 50 adjusts the laser beam LL for efficient acquisitionsof the EUV light so that its spot size and energy density on the targetT is necessary and sufficient to generate the plasma.

The plasma also generates the debris in addition to the EUV light, whichoriginates from the target T, copper, and target supply unit 60. Thegenerated debris gradually adheres to and deposits on the first opticalsystem 10, lowering the light intensity. Accordingly, the debrismitigation system 14 is arranged between the plasma emitting point PLand the first optical system 10. In addition, the second optical system30 omitted in FIG. 10 supplements the EUV light shielded by the debrismitigation system 14.

The illumination optical system 114 includes condenser mirrors 114 a,and an optical integrator 114 b. The condenser mirror 114 a serves tocollect the EUV light that is isotropically irradiated from the laserplasma. The optical integrator 114 b serves to uniformly illuminate thereticle 120 with a predetermined numerical aperture (“NA”). An apertureto limit the illumination area to an arc shape is also provided. Theillumination optical system 114 may use a multilayer mirror and angrazing angle total reflection mirror.

The reticle 120 is a reflection reticle that has a circuit pattern orimage to be transferred, and supported and driven by the reticle stage125. The diffracted light from the reticle 120 is reflected by theprojection optical system 130 and projected onto the object 140. Thereticle 120 and the object 140 are arranged in an optically conjugaterelationship. The exposure apparatus 100 is a scanner, and projects areduced size of the pattern of the reticle 120 onto the object 140 byscanning the reticle 120 and the object 140.

The reticle stage 125 supports the reticle 120 and is connected to amoving mechanism (not shown). The reticle stage 125 may use anystructure known in the art. A moving mechanism (not shown) may include alinear motor etc., and drives the reticle stage 125 at least in adirection X and moves the reticle 120. The exposure apparatus 100synchronously scans the reticle 120 and the object 140.

The projection optical system 130 uses plural multilayer mirrors 130 ato project a reduced size of a pattern of the reticle 120 onto theobject 140. The number of mirrors 130 a is about four to six. For wideexposure area with the small number of mirrors, the reticle 120 andobject 140 are simultaneously scanned to transfer a wide area that is anarc-shaped area or ring field apart from the optical axis by apredetermined distance. The projection optical system 130 has a NA ofabout 0.2 to 0.3.

The instant embodiment uses a wafer for the object 140, but it mayinclude a spherical semiconductor and liquid crystal plate and a widerange of other objects to be exposed. Photoresist is applied onto theobject 140.

The object 140 is held onto the wafer stage 145 by a wafer chuck 145 a.The wafer stage 145 moves the object 140, for example, using a linearmotor in XYZ directions. The reticle 120 and the object 140 aresynchronously scanned. The positions of the reticle stage 125 and waferstage 145 are monitored, for example, by a laser interferometer, anddriven at a constant speed ratio.

The alignment detection system 150 measures a positional relationshipbetween the position of the reticle 120 and the optical axis of theprojection optical system 130, and a positional relationship between theposition of the object 140 and the optical axis of the projectionoptical system 130, and sets positions and angles of the reticle stage125 and the wafer stage 145 so that a projected image of the reticle 120may be positioned in place on the object 140.

A focus detection optical system 160 measures a focus position on theobject 140 surface, and control over a position and angle of the waferstage 145 may always maintain the object 140 surface at an imagingposition of the projection optical system 130 during exposure.

In exposure, the EUV light emitted from the illumination apparatus 110illuminates the reticle 120, and images a pattern of the reticle 120onto the object 140 surface. The instant embodiment uses an arc or ringshaped image plane, scans the reticle 120 and object 140 at a speedratio corresponding to a reduction ratio to expose the entire surface ofthe reticle 120. The EUV light source 112 in the illumination apparatus110 used for the exposure apparatus 100 improves the light intensity andthe angular distribution of the exposure light, sufficiently removes thedebris, and stably generates the EUV light. Thus, the exposure apparatus100 may manufacture devices (such as a semiconductor device, a LCDdevice, an image-taking device (such as a CCD), and a thin-film magnetichead) with good economical efficiency and throughput.

Referring now to FIGS. 11 and 12, a description will be given of anembodiment of a device manufacturing method using the above exposureapparatus 100. FIG. 11 is a flowchart for explaining manufacture ofdevices (i.e., semiconductor chips such as IC and LSI, LCDs, CCDs,etc.). Here, a description will be given of a fabrication of asemiconductor chip as an example. Step 1 (circuit design) designs asemiconductor device circuit. Step 2 (reticle fabrication) forms areticle having a designed circuit pattern. Step 3 (wafer preparation)manufactures a wafer using materials such as silicon. Step 4 (waferprocess), which is referred to as a pretreatment, forms actual circuitryon the wafer through photolithography using the mask and wafer. Step 5(assembly), which is also referred to as a posttreatment, forms into asemiconductor chip the wafer formed in Step 4 and includes an assemblystep (e.g., dicing, bonding), a packaging step (chip sealing), and thelike. Step 6 (inspection) performs various tests for the semiconductordevice made in Step 5, such as a validity test and a durability test.Through these steps, a semiconductor device is finished and shipped(Step 7).

FIG. 12 is a detailed flowchart of the wafer process in Step 4. Step 11(oxidation) oxidizes the wafer's surface. Step 12 (CVD) forms aninsulating film on the wafer's surface. Step 13 (electrode formation)forms electrodes on the wafer by vapor disposition and the like. Step 14(ion implantation) implants ions into the wafer. Step 15 (resistprocess) applies a photosensitive material onto the wafer. Step 16(exposure) uses the exposure apparatus 100 to expose a circuit patternof the reticle onto the wafer. Step 17 (development) develops theexposed wafer. Step 18 (etching) etches parts other than a developedresist image. Step 19 (resist stripping) removes the disused resistafter etching. These steps are repeated, and multilayer circuit patternsare formed on the wafer. The device manufacturing method of thisembodiment may manufacture a higher quality device than the conventionalmethod. The device fabrication method that uses the exposure apparatus100 and the resultant devices also constitute one aspect of the presentinvention.

Further, the present invention is not limited to these preferredembodiments, and various variations and modifications may be madewithout departing from the scope of the present invention.

This application claims a benefit of priority based on Japanese PatentApplication No. 2004-295625, filed on Oct. 8, 2004, which is herebyincorporated by reference herein in its entirety as if fully set forthherein.

1. An X-ray generator for generating plasma and X-ray emitted from theplasma, said X-ray generator comprising: a unit for generating theplasma; and plural reflection optical systems for introducing the X-raythrough different optical paths.
 2. An X-ray generator according toclaim 1, wherein said plural reflection optical systems haveapproximately the same condensing point.
 3. An X-ray generator accordingto claim 1, wherein said plural reflection optical systems have thedifferent number of reflections.
 4. An X-ray generator according toclaim 1, wherein said plural reflection optical systems include: a firstreflection optical system that includes a spheroid mirror; and a secondreflection optical system that includes a spheroid mirror and ahyperboloid mirror.
 5. An X-ray generator according to claim 1, whereinsaid plural reflection optical systems include: a first reflectionoptical system that includes a spheroid mirror; and a second reflectionoptical system that includes plural mirrors each having a curvature. 6.An X-ray generator according to claim 1, further comprising a debrismitigation system for preventing debris generated at a light emittingpoint of the X-ray from reaching one of said plural reflection opticalsystems.
 7. An X-ray generator according to claim 6, wherein an opticalsystem among said plural reflection optical systems other than the oneenlarges a light intensity distribution at a condensing point of theX-ray formed by the one optical system, with respect to an angle from anoptical axis.
 8. An X-ray generator according to claim 6, wherein anoptical system among said plural reflection optical systems other thanthe one includes a rotationally symmetrical mirror.
 9. An X-raygenerator according to claim 1, wherein said X-ray has a wavelength of20 nm.
 10. An exposure apparatus comprising: an X-ray generatoraccording to claim 1; an illumination optical system for illuminating areticle having a pattern with X-ray generated by said X-ray generator;and a projection optical system for projecting the pattern of thereticle illuminated by said illumination optical system, onto an objectto be exposed.
 11. A device manufacturing method comprising the stepsof: exposing an object using an exposure apparatus according to claim10; and developing the object exposed.